1. Field of the Invention
The present invention relates to three-dimensional printing apparatuses and three-dimensional object printing methods.
2. Description of the Related Art
A three-dimensional printing apparatus known in the art cures a resin material so as to sequentially stack resin material layers each having a predetermined cross-sectional shape, thus printing a desired three-dimensional object. Using cross-sectional shape data indicative of cross-sectional shapes of a three-dimensional object to be printed, such a three-dimensional printing apparatus cures photo-curable resin so as to form resin layers whose shapes conform to the cross-sectional shapes. The three-dimensional printing apparatus sequentially stacks the resin layers conforming to the cross-sectional shapes, thus printing the three-dimensional object.
For example, JP 2003-39564 A discloses a three-dimensional printing apparatus including a tank storing photo-curable resin; a raisable and lowerable holder disposed above the tank; and a projector disposed below the tank and configured to project images. Each image presents a predetermined cross-sectional shape. The projector applies light presenting the cross-sectional shape onto the photo-curable resin in the tank, thus curing a portion of the photo-curable resin in the tank onto which the image is projected (i.e., the light is applied). Changing images to be projected allows curing of an appropriate portion of the photo-curable resin. This enables formation of a resin layer having a desired cross-sectional shape. Sequential raising of the holder allows resin layers to be formed continuously downward. Thus, a desired three-dimensional object is printed.
If an image projected from the projector is distorted in the tank, a resulting resin layer will not accurately conform to a predetermined cross-sectional shape presented by the image. To solve such a problem, JP 2015-7866 A discloses a technique for correcting an image to be projected from a projector so that the image is not distorted in a tank.
If an image projected from the projector is distorted in the tank, the image projected onto the tank will vary in brightness. This means that the image projected may have a large difference between the brightness value of a portion of the image and the brightness value of another portion of the image. Thus, photo-curable resin stored in the tank is cured to varying degrees. In other words, a portion of the photo-curable resin having a low brightness value will not be cured sufficiently. This insufficient curing may degrade the quality of a resulting three-dimensional object. One solution to distortion of an image projected from a projector may be to provide a mechanism to adjust the position and/or orientation of the projector. Unfortunately, providing such a mechanism increases the size of a three-dimensional printing apparatus itself and raises manufacturing costs thereof. The technique disclosed in JP 2015-7866 A does not reduce or eliminate brightness variations of an image projected onto the tank.